The present invention relates generally to scan mechanisms for imaging systems, and, more particularly, those used in combined downward and forward looking infrared line scanners.
Infrared Line Scanners ("IRLS") for downward viewing from aircraft are well-known and are routinely used for aerial reconnaissance and for earth resources studies. Similarly, Forward Looking Infrared Line Scanners ("FLIRS") are also well known, and are commonly used as reconnaissance or night vision devices. In other applications, for example reconnaissance from a remotely piloted or autonomously guided vehicle, it is often necessary to provide the means of viewing in either the downward or forward direction depending on the immediate mission requirements. In such vehicles it is also often necessary to point the line of sight of the sensor or scanner in a particular direction, and to stabilize that line of sight against motions due to either aircraft maneuver, undesirable vibration or buffeting motions which commonly occur during flight. Currently, FLIR sensors are available which provide stabilization and pointing relative to the aircraft axes.
Where both downward and forward looking capabilities are necessary on the same aircraft, a single sensor/scan mechanism is most desirable since space and weight are limited on such aircraft. However, a single sensor generally cannot be simply gimbal-mounted such that the sensor is slued from forward to downward looking mode. First, it may take too long to slue the sensor from one line of sight to another. Second, the fields of view of either sensor type are generally incompatible. For example, the small rectangular field of view of a FLIR would not be particularly useful in a downward viewing mode where wide across track or horizon to horizon coverage typically provided by an IRLS sensor are most desirable.
It is accordingly a primary object of the present invention to provide an improved electro-optical scanning mechanism capable of selectively viewing either of two scenes of interest and which uses a common optical path and common elements to minimize sensor size, weight, cost and complexity.
A further object of the present invention is to provide such a scanning sensor which can be easily switched from one viewing mode to another in a minimum amount of time and with minimum sensor motion.
It is a further object of the present invention to provide a sensor capable of rapid and efficient stabilization in one axis (for example, in the aircraft pitch axis) without the need of gross motion of the entire sensor, thereby further reducing system complexity, weight and cost.